Dinitrosyl iron complexes [E5Fe(NO)(2)](-) (E = S, Se): A precursor of Roussin's black salt [Fe4E3(NO)(7)](-)

摘要

[PPN][Se5Fe(NO)(2)] (1) and [K-18-crown-6-ether][S5Fe(NO)(2)] (2') were synthesized and characterized by IR, UV-Vis, EPR spectroscopy, magnetic susceptibility, and X-ray structure. [PPN][Se5Fe(NO)21 easily undergoes ligand exchange with S-8 and (RS)(2) (R = C7H4SN (5), o-C6H4NHCOCH3 (6), C4H3S (7)) to form [PPN][S5Fe(NO)(2)] and [PPN][(SR)(2)Fe(NO)(2)]. The reaction displays that [E5Fe(NO)(2)](-) (E = Se (3), S (4)) facilely converts to [Fe4E3(NO)(7)](-) by adding acid HBF4 or oxidant [Cp2Fe][BF4] in THF, respectively. Obviously, complexes 1 and 2' serve as the precursors of the Roussin's black salts 3 and 4. The electronic structure of {Fe(NO)2)9 core of [Se5Fe(NO)(2)](-) is best described as a dynamic resonance hybrid of {Fe+1(-NO)(2)}(9) and {Fe-1(NO+)(2)}(9) modulated by the coordinated ligands. The findings, EPR signal of g = 2.064 for 1 at 298 K, implicate that the low-molecular-weight DNICs and protein-bound DNICs may not exist with selenocysteine residues of proteins as ligands, since the existence of protein-bound DNICs and low-molecular-weight DNICs in vitro has been characterized with a characteristic EPR signal at g = 2.03. In addition, complex 2' treated human erythroleukemia K562 cancer cells exposed to UV-A light greatly decreased the percentage survival of the cell cultures. (c) 2006 Elsevier B.V. All rights reserved.